Amazon’s plans to add text to audiobooks is at risk, after major book publishers filed a lawsuit claiming it is a violation of copyright law.

Amazon’s hugely successful audiobook platform Audible last month announced Audible Captions, which utilises machine learning and AI to transcribe an audio recording for listeners, allowing them to read along with the narrator.

While Amazon says it is similar to the function of subtitles on a movie or television show, opponents have argued this makes the text less like an audiobook and more like a book.

And this, according to leading publishers Hachette, HarperCollins, Macmillan, Penguin Random House, and Simon & Schuster, is illegal.

“Audible Captions takes Publishers’ proprietary audiobooks, converts the narration into unauthorized text, and distributes the entire text of these “new” digital books to Audible’s customers,” the lawsuit claims.

“Audible’s actions—taking copyrighted works and repurposing them for its own benefit without permission—are the kind of quintessential infringement that the Copyright Act directly forbids.”

The publishers also claim Amazon has gone ahead with the plans without any notice or consultation with the publishers.

Physical books and ebooks have separate licenses. The publishers are arguing Amazon is attempting to produce physical books without the appropriate rights.

Amazon has disputed this.

“It is not and was never intended to be a book,” the company said in a statement.

“We disagree with the claims that this violates any rights and look forward to working with publishers and members of the professional creative community to help them better understand the educational and accessibility benefits of this innovation.”

Audible Captions is set to launch next month.